Generally, a plasma processing apparatus is known as a single wafer process apparatus for applying a predetermined treatment, such as etching, CVD (chemical vapor deposition), or sputtering, to a semiconductor wafer.
In this type of plasma processing apparatus, various treatments are applied to a semiconductor wafer at a relatively high temperature, with the semiconductor wafer being placed on a susceptor in a processing vessel in which a vacuum can be produced. During any of the treatments, it is necessary to maintain the wafer so that its position does not deviate. For this purpose, an electrostatic chuck is generally used.
A conventional general plasma processing apparatus will be described. FIG. 11 is a schematic configurational view showing a conventional and general plasma processing apparatus. In a processing vessel 2 that can be sucked, a susceptor 4 concurrently serving as a lower electrode is mounted. The susceptor 4 has a heater 6, such as a sheath heater, buried therein in an insulated state. Concretely, the heater 6 is cast, for example, in aluminum, and buried therein. Onto an upper surface of the susceptor 4 made of aluminum, a ceramic electrostatic chuck 8 is joined by means of an adhesive, the electrostatic chuck 8 comprising a chuck electrode buried in a ceramic material, the chuck electrode for use in electrostatic chucking. A semiconductor wafer W is attracted to and held on an upper surface of the electrostatic chuck 8 by an electrostatic force.
In a ceiling portion of the processing vessel 2, an upper electrode 10 is provided to face the susceptor 4. In the upper electrode 10, a heater 12, such as a sheath heater, is cast in aluminum or the like, and buried therein. Connected to the upper electrode 10 is a high frequency power source 14 for applying a high frequency voltage for plasma generation. A plasma is generated between the upper electrode 10 and the susceptor 4 as a lower electrode to perform a predetermined treatment for the wafer W.
When the treating temperature for the semiconductor wafer is relatively low, e.g., about 200° C. or lower, no particular problem occurs. However, raising the treatment temperature, for example, to about 300 to 400° C. is demanded in order to increase the treating rate, such as film deposition rate, or to improve the quality of the resulting film.
For example, in connection with the upper electrode 10, in such a high temperature region, the amount of thermal expansion and contraction due to a temperature rise and a temperature fall during treatment, or thermal stress is considerably great. Thus, warpage or deflection may occur in the electrode itself, posing the problem of making high frequency propagation for plasma generation nonuniform. A shower head for gas supply may be attached, in close contact, to a lower surface of the upper electrode 10. For the reasons stated above, cracking may occur in the shower head.
In connection with the susceptor 4, the electrostatic chuck 8 may peel off because of heat exceeding the limits of heat resistance of the adhesive, or warpage or deflection may occur in accordance with the occurrence of thermal expansion and contraction, or thermal stress stated above. Besides, the problem may arise that the electrostatic chuck 8 itself cracks owing to the difference in the coefficient of linear thermal expansion between the aluminum constituting the susceptor 4 and the ceramic constituting the electrostatic chuck 8.
Particularly as the wafer size increases from 6 inches to 8 inches, further to 12 inches, the amount of thermal expansion and contraction becomes large correspondingly. Thus, early solutions to the above-described problems are desired.